Process for separating phosphorus and like elements from ores



March 14, 1939. H. A, BLAcKwl-:LL ETAL 2,150,261

PROCESS FOR SEPABTNG PHOSPHORUS AND LIKE ELEMENTS FROM CRES Filed Novf 26, 1937 UNITED sTATEs PATENT OFFICE PnocEss Fon. sEPAnA'rmG PnosPnoRUs AND LIKE ELEMENTS Faoin omis Harold Alexandre Blackwell and William Lawrence Turner, Garston, Liverpool, England Application November 2s, 1937, serial No. 116,754

In Great Britain December 10, 1936 7 Claims. (Cl. 75-10) This invention is for an improved process for ing from the still so as to permit of sampling of separating phosphorus and like elements from the gases resulting from the reaction. ores orv compounds containing phosphorus, for For a cylindrical still of about 3% metres in example, iron ores. .The elements like phosdiameter and 41/2 metres in height, 12 high frephorus included in the invention are those which quency induction copper tube coils I3 are eml are solids at N. T. P. and-are set out in the horiployed, each coil being associated with a thermzontal line, seriesf3, of the periodic table in which ionic valve oscillator in accordance with known phosphorus is classified, and comprise' sodium, practice. f The bank of oscillators is indicated at silicon, sulphur and aluminium. l I4 and the induction coils are connected thereto ,From one point of view the present invention by insulated terminal fittings I5 and leads I8. 10 consists in separating phosphorus and like ele- The exterior of the still is coated with a heatments which sublime at low temperatures from resisting paint I1 to seal the still against penetraores containing such elements and in which the tion of outside air. metal in the ore has a relatively high boiling The central coke core 4 in the still has a pyrompoint compared with phosphorus. eter I8 or` thermostat embodied therein and 15l From another point of view the invention proconnected to the oscillation generator I4'by leads vides a process for producing non-phosphoric pig I9 so that the energy supplied to the induction iron from iron ore, and under certain circumcoil can be controlled in accordance with the temstances silicon-freepig iron from iron ore having perature of the heat generator in the still. If

a substantial proportion (for example 13%) of desired a. thermostatic control of the current sup- 20 silicon present in the ores as quartz and silicates plied to the coil may be arranged by locating a. of iron. thermostat at or near the draw-off aperture 3 The apparatus employed for effecting the sepin the upper part of the still so that the temperaaration of phosphorus and like elements as above ture of the outgoing gases exercises control. o described from their ores formsno part of the Thehigh frequency induction is generated by 25 present invention. One typical apparatus in an oscillator, such as a thermionic valve, capable which the invention may be carried out is shown of providing a frequency Which Will quickly raise diagrammatically in the accompanying drawthe grephlte reducing agent 0f the Charge to ing and comprises a closed fire-brick still I of a red heat, and the frequency must be higher cylindrical shape having a tapping aperture 2 than 3000 cycles per second (where the sub-di- 30 in its base and a draw-off aperture 3 in its upper vided graphite has a granular size of 3A diportion. Located centrally of the still is a heat ameter) otherwise the graphite will not be raised generator or primer 4 comprising a coke core to a temperature-Capable 0f reducing phOSDhOruS built up with granular coke of a granular size of from the iron ore. The preferred frequency is about 3A" diameter. The draw-oil aperture 3 much higher than 3000 cycles per second and is 35 in the upper part of the still is connected by a of the order of 300,000 cycles per second. valve-controlled conduit 5 to a condenser which, One example of the process will now be de- When phosphorus has to be recovered conprises scribed. 30 lbs. of low grade iron ore containing a closed water tank 6 andbeneath the free surapproximately 32% 0f iI'On, .13% epatite (P205),

face 'I of the Water in the tank is led the outlet 13% Silicon (as quartz end slllcales df idn) 23% 40 conduit 5 from the still. The free space above sulphur' and the balance m lmpllritles" 1S mixed the Water in the tank is continuously evacuated with a quantity 0f Sub'dlvlded coke Whlh iS 20% by. a suction pump 8 and the water in the tank is in excess of the approximate chemical balance for v cooled by, say, a submerged coil 3 so las to proreduction of the iron and the impurities. The mote the condensation of phosphorus in the foot mix iS Charged into the Still by removing the deof the tank from 'which it can be tapped off tachable cover 2d; and after charging has been through an outlet aperture lo. other unwanted completed the cover is replaced and the tapping gases bubble through the water and are extracted aperture is sealed by the usual plug of ganister by the pump. A by-pass conduit II extends beand a binder. The suction pump is first con# tween the conduit leading from the still to the nected to the still and a pressurerof 50 mm. 50 inlet of the suction pump, and this conduit ls (barometric) is established inside the still. The valve-controlled so that the passage of the gases vacuum in the still is maintained at about 50 mm. from the still can be directed either into the The still is then connected to the condenser. The condenser or directly to the exhaust pump. A furnace is `started up and the valves tuned in un.-

sampling cock I2 is provided in the conduit leadtil the furnace is operating at 300,000 cycles per 55 second. After a short time an intense heat is generated in thecoke, and a considerable evolution of gases takes place. 'I'hese bubble through the water in the condenser and are drawn oft by the pump. 'Ihe temperature is maintained above the boiling point of phosphorus, 'but below the boiling point of iron, preferably at 600 C. This temperature of 600 C. is thermostatically maintained. A sample of the evolved gases is taken at the sampling cock and when evolution of phosphorus vapour has ceased the condenser is cut out and the gases are led directly to the exhaust pump. The vacuum in the still is maintained but the thermostat is rendered inoperative no phosphorus or silicon in the pig iron. 2% ozs.

silicon,

of substantially pure phosphorus were recovered from the Water in the condenser.

It is thought that since the reduction was car'- ried on at a temperature of approximately 600 C. the phosphorus is reduced and distilled over into the condenser and the silicates separate from the iron and oat on the iron when it is subsequently made molten in an unsintered condition, l

and that therefore although the silicates are not reduced or distilled they are freed from the iron in the still.

An example of the invention as applied to the reduction of aluminium from bauxite is as follows:

A mixture of nely divided bauxite and coke in 1A grains in the proportion 2 parts by weight bauxite to 1 part by weight coke is placed in a dish or crucible of fused alumina. The air is exhausted from the still until a pressure of 20 mm. is established inside the still. The high frequency induction is started up and operating at 380,000 cycles per second, the charge is heated to a temperature above the boiling point of aluminium, and bright aluminium metal is recovered on condensation.

Shock cooling of the vaporized aluminium may be employed for example in small scale' operations it is possible to coat a cooled surface of glass with mirror-bright aluminium metal by subliming the metal on to the glass in the still.

In recovering sublimed silicon the procedure is as follows:

Approximately 8 parts by weight quartz dust (98.75% SiOz) is mixed with 3 parts by weight coke of approximately lo" in grain. The mix is put into a sillimanite crucible and an internal vacuum of 76 mm. established in the still. The charge is heated by high frequency induction of 380,000 cycles per second to above the 'boiling point of silicon, and a recovery of approximately 4 parts by weight brilliant silicon crystals (98.9%

Silicon) is recovered on condensation.

Owing to the tendency for aglow discharge to be generated inside the still under high vacuum and in the presence of substantial quantities of carbon monoxide (which are produced with silicon reduction) the pressure inside the still must be controlled accordingly to a-void such glow discharge and, for silicon, is not lower than 76 mm.

We claim:

1. A process for separating phosphorus, sodium, sulphur or aluminium from compounds containing any one of the aforesaid elements, which comprises mixing the compounds with a quantity of graphitic carbon, as reducing-agent, in excess of that required to reduce the element present in the compound and heating the mix by high frequency induction to a temperature above the boiling point of the element butbelow the boiling point of the compound in which the element is contained in a closed still maintained at a barometric pressure not'higher than 180 mm. and distilling the element from the reaction mix without liquefaction of the mix, and continuously extracting from the still the gases resulting from the reaction and separating the element from the extracted gases by fractional condensation.

2. A process for separating phosphorus from ores containing phosphorus which comprises mixing the ores with a quantity of graphitic carbon, as reducing-agent, in excess of that required to reduce the phosphorus present in the ores and heating the mix by high frequency induction to a temperature of about 600 C. in a closed and sealed still maintained at a barometric pressure not higher than mm. and distilling the phosphorus from the reaction mix without liquefaction of the mix, and continuously extracting from the still the gases resulting from the reaction and separating the phosphorus from the extracted gases by condensation under Water. l 3. 4A process for separating phosphorus from low grade phosphoric iron ore which comprises mixing the ore with graphitic carbon and heating the charge by high frequency induction in a closed still at a temperature of about 600 C. and under a pressure not higher than 180 mm. barometric pressure, continuously evacuating the gases resulting from the reaction and discharging them under cooled water to eliminate the vaporized phosphorus, and, after the evolution of vaporized phosphorus has ceased, `lay-passing the gases directly to the evacuating means and increasing the temperature of the residual mass until the iron is in a molten condition and tapping off the molten metal from the still.

4. A process for separating phosphorus from low grade phosphoric iron ore which comprises mixing the ore with graphitic carbon of granular size approximating to and heating the charge by high frequency induction of the order of 300,000 cycles per second in a sealed still and located aroundL a graphitic carbon core to a temperature of about 600 C. and under a pressure not higher than 50 mm. barometric pressure, maintaining the said temperature thermostatically, continuously evacuating the gases resulting from the reaction and discharging them under cooled water to eliminate the vaporized phosphorus, and after the evolution of vaporized phosphorus has ceased, cutting out the thermostatic control of the temperature, by-passing the gases directly to the evacuating means, and increasing the temperature of the residual mass until the iron is in a molten condition, and tapping ofi the molten metal from the still.

5. A process for separating aluminium from its compounds which comprises mixing the aluminium compound with graphitic carbon and heating the charge by high frequency induction of the order of 300,000 cycles per second in a sealed still and under a pressure not higher than 180 mm. barometric pressure, and. subliming the metallic aluminium from the mix.

6. A process for separating aluminium from bauxite which comprises mixing the bauxite in a finely divided condition with iinely divided graphitic carbon, and heating the charge by high con compound in a nely diyidedv condition with frequency induction of not less than 300,000 cycles per second in a. sealed still and under a pressure of the order of 20 mm. barometric pressure and to a temperature below the fusion point of bauxite but above the boiling pointof aluminium, continuously evacuating the gases resulting from the reaction and separating the aluminium from the extracted gases by fractional condensation.

7. A process for separating silicon from compounds of silicon which comprises mixing the sili- 

